Multifunctional Antennas and Arrays for Wireless Communication Systems. Группа авторов

structure is radiating, it has little effect on the upper band antenna. The outer rectangular length and width are R_L = 25 mm and R_W = 22.25 mm. The rectangular slot cutout (slot length of S_L = 15 mm and a slot width of S_W = 5.125 mm) dimensions are noted. The centerline feed has a length and width of F_L = 19.5 mm and F_W = 3 mm. Photograph of this antenna is shown in Figure 1.14 with an overall substrate size of length L₁ = 80 mm and width W₁ = 60 mm. The material used was FR‐4 (ε_r = 4.4) with a thickness of t = 0.762 mm. Response of this antenna can be found in [5] and hence is not repeated here.

As a reconfigurable antenna, the lower band meandered antenna also includes a biasing network. The DC biasing lines are placed on the same side as the ground plane (Figure 1.12), so as to limit the effect of coupling. The DC biasing lines include a RF choke inductor to block any high‐frequency signal from entering the DC power supply. A current limiting resistor is also added to the positive voltage terminal to protect the varactor diode. On the top side of the antenna where the radiating structure is located, a single DC blocking capacitor is placed above the varactor diode such that the potentially damaging DC supply voltage does not enter the RF signal. For the varactor diode, the reverse biasing voltage is varied from 0 to 20 V which varies the capacitance from 13.3 to 0.69 pF, respectively.

Figure 1.13 Surface current distribution with capacitance of 1.6 pF: (a) 810 MHz and (b) 1.68 GHz.

      Source: Damman et al. [5].

Figure 1.14 Photograph of the fabricated single‐feed dual band antenna: (a) top view and (b) bottom view.

      Source: Damman et al. [5].

      Although mechanisms to achieve frequency reconfigurable and frequency agile/tunable antenna are different, for our discussion, we refer both antennas under the “Reconfigurable Antenna,” category.

1.8 Antenna Measurements

Antenna performance parameters measurement is important for verifying computation, simulation, and analysis results. For measuring circuit parameters such as scattering parameters (S_ii/S_ij), where S_ii and S_ij refer to self‐port reflection coefficient and coupling port transmission coefficient, vector network analyzers are preferred after proper calibration [6]. For example, Figure 1.15 shows photographs of vector network analyzers from Anritsu and Keysight, both of which are available at the Antenna and Microwave Laboratory (AML), San Diego State University.

For measuring radiation patterns, we can use far‐field, near‐field, and compact antenna test range (CATR) chambers. Figure 1.16 shows photographs of the far‐field and CATR anechoic chambers at the AML, San Diego State University. The first anechoic chamber is shown in Figure 1.16a, which is capable of far‐field radiation measurements. It can cover a frequency range from 800 to 40 GHz. The chamber comes with ORBIT/FR 959 acquisition measurement software and provides measurement results for 2D/3D radiation pattern, realized gain, and polarization with sense of rotation.

      The Mini‐Compact Antenna Test Range (M‐CATR) from Microwave Vision Group (MVG) for millimeter‐wave antenna measurement covers frequencies between 26.5 and 110 GHz, as shown in Figure 1.16b. Keysight N5225A Power Network Analyzer (PNA) serves its signal power generator that ranges from 10 to 50 GHz. The frequency is extended up to 110 GHz using proper external frequency extenders: V‐band (50–75 GHz) and W‐band (75–110 GHz). This chamber is capable of measuring realized gain, 2D and 3D radiation patterns, and polarization of the antenna with the sense of rotation using the ORBIT/FR 959 acquisition measurement software.

      Interested readers should review text books on the theory behind antenna radiation pattern measurements such as [1].

Figure 1.15 Vector network analyzer (VNA) can be used for measurement of the scattering parameter: (a) Anritsu's VNA and (b) Keysight's VNA.

Figure 1.16 Antenna testing in anechoic chamber at the Antenna and Microwave Laboratory (AML), San Diego State University: (a) far‐field anechoic chamber covering 800–40 GHz and (b) Mini‐Compact Antenna Test Range (M‐CATR) system covering 26.5–110 GHz.

1.9 Conclusion

      This chapter introduced basics of antennas as well as an introduction to reconfigurable, multifunctional, frequency agile/tunable, and antenna measurements. In the coming chapters, we dive into a more detailed discussion.

References

      1 1 Balanis, C.A. (2016). Antenna Theory: Analysis and Design, 4e. Wiley.

      2 2Babakhani, B. and Sharma, S.K. (2015). Wideband frequency tunable concentric circular microstrip patch antenna with simultaneous polarization reconfiguration. IEEE Antennas and Propagation Magazine 57 (2): 203–216.

      3 3 Sharma, S.K. and Wang, A. (2018). Two elements MIMO antenna for tablet size ground plane with reconfigurable lower bands and consistent high band radiating elements. 2018 IEEE International Symposium on Antennas and Propagation & USNC/URSI National Radio Science Meeting, Boston (8–13 July 2018).

      4 4 Wang, A. (2017). Four elements compact MIMO antenna with reconfigurable lower band and consistent high band for tablet applications. MS (Electrical Engineering) Thesis. San Diego State University.

      5 5 Damman, R., Mishra, G., Sharma, S.K., and Babakhani, B. (2017). A single feed planar antenna with 4G tunable bands and consistent upper LTE bands between 1.29 GHz–2.05 GHz. Microwave and Optical Technology Letters 59 (8): 2070–2075.

      6 6 Pozar, D.M. (2011). Microwave Engineering, 4e. Wiley.